In an article entitled Alternative Systems For Rapid Transit Propulsion And Electrical Braking, published in the Westinghouse Engineer for March, 1973, at pages 34-41, there is described a thyristor chopper control system for propulsion and electrical braking of transit vehicles. The thyristor chopper provides a propulsion system that is superior in smoothness and ease of maintaining a given speed, which latter feature is desired for automatic train control.
It is known in the prior art to operate a vehicle propulsion motor with a programmed microprocessor controlling a chopper that determines the average current of that motor as described in the above cross referenced patent application and in U.S. Pat. No. 4,095,153 of T. C. Matty, et al.
It is known in the prior art to provide a slipslide control system for a vehicle, such as a transit car, as described in an article published in The Westinghouse Engineer for September, 1970 at pages 143-149, wherein once a pair of wheels is slipping or sliding then corrective action is taken to reduce the tractive or braking effort applied to the axle to permit those wheels to regain the speed equivalent to train speed. The desired tractive or braking effort is then reapplied.
U.S. Pat. No. 3,069,606 discloses the utilization of an auxiliary field for a DC traction motor arranged in a bridge circuit and operative with a train vehicle to respond to differences in the speeds of selected motors to limit the motor speed for protecting a motor against excessive voltage and excessive speed.
U.S. Pat. No. 3,783,339 discloses the provision of two tachometers coupled with a moving vehicle, such that the output of a first tachometer leads the signal provided by the second when the vehicle is traveling forward and the output of the second tachometer leads the signal provided by the first when the vehicle is traveling in a reverse direction, for the purpose of controlling the movement of the vehicle.